The present invention broadly relates to a casting machine such as a cold chamber type diecasting machine, and more particularly to an electromagnetic pump type automatic molten-metal supply apparatus having a molten-metal supply amount control device adapted to vary the molten-metal supply period so as to compensate for any change in height of the surface of the molten-metal within the molten-metal tank.
In a casting machine such as a cold chamber type diecasting machine, the method of supplying molten metal to the mold that has long been practiced is the one in which the operator handling the casting operation draws up a certain amount of molten metal by a ladle and pours it into the mold. However, this method is disadvantageous in terms of the labour required and the level of precision possible. Therefore, an electromagnetic pump type automatic molten-metal supply apparatus has recently been developed. Such an apparatus has encountered problems concerning what should be done to compensate for changes in static pressure that are caused by change in height of the surface of molten metal within the molten metal tank and for changes in volume of molten metal within the molten-metal supply pipe so that a constant amount of molten metal can be supplied to the mold. In order to maintain the height of the surface of the molten metal within the tank at a constant level, it has been the practice, for instance, to frequently add molten metal by man-powered operations, or to measure the weight of cast products from time to time and manually adjust the timer which sets the molten-metal supply period in such a manner that the weight of cast products will be kept constant. However, such man-powered operations or manual adjustment of the period set in the timer is very cumbersome, and yet is not accurate enough in spite of he fact that a great deal of labour is required. Therefore, it has become essential to enable automatic control. In addition, such a device which performs suitable automatic control should not involve any complicated arrangement for enabling molten metal to be supplied in a constant amount each time nor require any cumbersome operation; instead, it is required to have a simple arrangement and to operate accurately.
An electromagnetic pump type automatic molten-metal supply apparatus is further required to have a structure that meets the following requirements. In an apparatus of this type, molten metal is supplied from the molten metal tank to the cold chamber of an injection cylinder of the diecasting machine through the molten-metal supply pipe by the operation of the pump. Since molten metal at a high temperature is supplied, it is necessary for the molten-metal supply pipe to be made of a material of high quality and with high precision. In addition, the overall structure of the apparatus should be such that the difference in temperature between molten metal in the cold chamber and molten metal in the molten-metal supply pipe causes no damage to the product, and, simultaneously, such that a certain amount of molten metal can be supplied accurately each time.